1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to audio signal coding, and more particularly, to tracking of sinusoids in parametric coding.
2. Description of the Related Art
Parametric coding is an audio signal coding method used for a monaural signal. The parametric coding conforms to the moving picture experts group (MPEG)-4 standard.
FIG. 1 is an illustration for explaining a parametric coding method. In the parametric coding method, an input signal is analyzed and parameterized. The input audio signal is first subject to an audio reading and filtering process, followed by a transient analysis, a sinusoidal analysis, and a noise analysis. As a result, parameters of respective audio components are extracted. The transient analysis is provided to compensate for significantly dynamic changes in the audio signal. The sinusoidal analysis is provided to compensate for deterministic changes in the audio signal. The noise analysis is provided to compensate for stochastic or non-deterministic changes in the audio signal.
The extracted parameters are subject to a bit-stream formatting process.
Methods and apparatuses consistent with the present invention particularly relate to the sinusoidal analysis. A sinusoid, also referred to as a partial, is generated as a result of the sinusoidal analysis.
In the parametric audio coding, after the sinusoid analysis is performed, the sinusoid is subject to an adaptive differential pulse code modulation (ADPCM) or a differential pulse code modulation (DPCM). To this end, partials (sinusoids) have to be tracked.
A conventional tracking method employs only two modes, a birth mode and a continuation mode.
The continuation mode is set when one partial has a correlation with another partial of a previous frame (this is referred to as being continued). Once the continuation mode is set, coding may be carried out using information on partials of the previous frame. Thus, the number of bits required for coding decreases.
On the other hand, with respect to the remaining partials which are not set to the continuation mode, the birth mode is set. Once the birth mode is set, a large number of bits are required to code the partials. Thus, coding efficiency deteriorates.
In the conventional method, one partial can be tracked by only another partial. Thus, even when a plurality of similar partials are continuously arranged with respect to one partial of a previous frame, the remaining partials which are not set to the continuation mode have to be set to the birth mode, which requires more bits.